Eric Sembrat's Test Bonanza

Development of laser-based techniques to cool and manipulate trapped atoms led to a quantum revolution, with applications ranging from creation of novel phases of matter to realization of new tools for navigation and timekeeping. Because of their comparatively richer internal structure, molecules offer additional potential for quantum-controlled chemistry, quantum information processing, and precision spectroscopy. However, obtaining control over the rotational quantum state of trapped molecules, a prerequisite for most applications, has presented a significant challenge because of the large number of initial states typically populated and because of unwanted excitations generally occurring during optical manipulation. Using a single spectrally filtered broadband laser simultaneously addressing many rotational levels, we have optically cooled trapped AlH+ molecules from room temperature to 4 Kelvins, corresponding to an increase in ground rotational-vibrational state population from 3% to 95%. We anticipate that the cooling timescale can be reduced from 100 milliseconds to a few microseconds and that the cooling efficiency can also be improved. Our broadband cooling technique should also be applicable to a number of other neutral and charged diatomic species. Trapped AlH+, in particular, is a good candidate for future work on ultracold chemistry, coherent control and entanglement of rotational quantum states, non-destructive single-molecule state readout by fluorescence, and searches for time-variations of the electron-proton mass ratio.

In the mid 60's, theoretical physicists came to the conclusion that a strong magnetic field could lead to a superconducting state where magnetism and superconductivity are interleaved on the nano-scale: tidal wave like domain walls spontaneously form in the superfluid order, trapping unpaired spins. Over the past 50 years, our theoretical understanding of this proposal has greatly advanced, yet we still have not found definitive experimental evidence of the modulated superconducting state (also known as the FFLO state, after the initials of the theorists who anticipated it). I will describe the current state of this search, with a particular focus on how experiments with ultracold atoms are about to find it.

Human and animal societies are exemplars of complex adaptive systems. Through multiple interactions between society members, they dynamically organize themselves and integrate information over multiple scales, both above (environmental) and below (genetic, physiological) the individual level. In the past 25 years, researchers across a range of fields including statistical physics, network theory and behavioral ecology have made enormous progress in understanding the positive and negative consequences of these multi-scale, self-organizing coordination mechanisms. I will present key concepts in the field of collective animal and human behavior, and review recent results from both theoretical and empirical studies conducted in my laboratory on ant colonies, slime mold cultures and human crowds. In particular I will discuss the role of interactions between group members and with their environment, the mechanisms by which information is transferred by and integrated into a population, and the consequences of functional and dysfunctional group dynamics.

This is a Webinar

Geographic tongue (GT) is a medical condition affecting approximately 2% of the population, whereby the papillae covering the upper part of the tongue are lost due to a slowly expanding inflammation. The resultant dynamical appearance of the tongue has striking similarities with well known out-of-equilibrium phenomena observed in excitable media, such as forest fires, cardiac dynamics and chemically driven reaction-diffusion systems. We explore the dynamics associated with GT from a dynamical systems perspective, utilizing cellular automata simulations. Our results shed light on the evolution of the inflammation and suggest a practical way to classify the severity of the condition, based on the characteristic patterns observed in GT patients.

 TBD

Fivefold symmetry is incompatible with the translational order in all 17 plane groups and is therefore of fundamental interest for two dimensional crystallization processes. A model study on single crystal surfaces, e.g. Cu(111), has been carried out to better understand the fundamental principles of intermolecular interactions between fivefold symmetric corannulene and its derivatives in two-dimensional clusters and lattices, including those consisting of fivefold bowl-shaped (buckybowl) molecules. Rational molecular design and state of the art surface science methods, e.g. Scanning Tunneling Microscopy, Low Energy Electron Diffraction, X-Ray Photoelectron Spectroscopy, Ultraviolet Photoelectron Spectroscopy, Temperature Programmed Desorption, and Reflection Adsorption Infrared Spectroscopy were applied. Several reversible surface phases were identified, including stripes, zig-zag, rosette and rotator phases. The packings of fivefold symmetric molecules was found to exhibit the same patterns upon adsorption as identified in the closest packings of hard pentagons and five-pointed stars.

Understanding the thermal conductivity of bulk crystalline solids is essentially a solved problem and it is well described by the phonon gas model (PGM). The PGM treats individual phonons (e.g., quanta of lattice vibration energy) as gas molecules that carry energy at a certain speed for some averaged distance, termed the mean free path (MFP). This model does an excellent job at explaining the thermal conductivity of crystalline solids and due to advancements in modeling over the last decade, one can now calculate phonon energies, velocities and MFPs fully from first principles. This now allows one to predict the thermal conductivity of virtually any crystalline material with excellent agreement with experiments at virtually all temperatures of technological interest. By employing Monte Carlo methods or the Boltzmann Transport Equation, one can also accurately predict the thermal conductivity of micro and nanostructures due to quantum or classical size effects. As a result of the great success of this model, it has prevailed as the primary physical picture used to understand and interpret all phonon transport related phenomena. However, there are a number of technologically important material classes and molecules that are not well described by the PGM. This talk will discuss several instances where the PGM is inconsistent with the atomic level behaviors observed in molecular dynamics simulations. The talk will also cover several new theoretical modeling developments that offer a different perspective on phonon-phonon interactions and allows for direct calculation of phonon contributions to thermal conductivity and interface conductance.

Metamaterials are commonly viewed as artificially-structured media capable of realizing arbitrary effective parameters, in which metals and dielectrics are delicately combined to facilitate the index contrast and plasmonic response required for a particular purpose. We aim to drive beyond this limited vision and explore the use of optical metamaterials as a generalizable platform for optoelectronic information technology: Metals will provide tailored plasmonic behavior as before, but will serve double duty by providing electrical functions including voltage input, carrier injection/extraction, and heat sinking, and dielectrics will consist of functional elements such as Kerr materials, electrooptic polymers, and p-n junctions. In this talk I will discuss our preliminary results on several topics in this category, including the electrically induced harmonic generation and optical rectification of light in a perfect metamaterial absorber, the nonlinear spectroscopy and imaging from a chiral metamaterial, and the backward phase-matching in an optical metamaterial where the fundamental and frequency-doubled waves possess opposite indices of refraction.

Biography

Wenshan Cai received his B.S. and M.S. degrees in Electronic Engineering from Tsinghua University, Beijing, China in 2000 and 2002, respectively, and his Ph.D. in Electrical and Computer Engineering from Purdue University, West Lafayette, Indiana, in 2008. He joined the faculty of the Georgia Institute of Technology in January 2012 as an Associate Professor in Electrical and Computer Engineering, with a joint appointment in Materials Science and Engineering. Prior to this, he was a postdoctoral fellow in the Geballe Laboratory for Advanced Materials at Stanford University. His scientific research is in the area of nanophotonic materials and devices, in which he has made a major impact on the evolving field of plasmonics and metamaterials. Dr. Cai has published ~40 papers in peer-reviewed journals, and the total citations of his recent papers have reached ~4,000 within the past few years. He is a reviewer or editorial board member of over 20 scientific journals. In addition, Dr. Cai is the lead author of the book Optical Metamaterials: Fundamentals and Applications (Springer, 2010), a text or a major reference used at many universities around the world, for which he won the 2014 Joseph W. Goodman Book Writing Award from OSA and SPIE.

The nature of dark matter remains one of the most fascinating yet unsolved problems in modern science. A large compelling body of evidence supports the theory that almost 27% of the mass-energy density of the universe is made of cold dark matter. The XENON Project aims at the direct detection of dark matter in the form of Weakly Interacting Massive Particles (WIMPs) via nuclear recoils in a LXe Dual-phase Time Projection Chamber. The third phase of the project XENON1T, a ton scale LXe dark matter detector is currently under construction at the Laboratori Nazionali del Gran Sasso in Italy and aims to achieve unprecedented sensitivities of the cross section of the WIMP-nucleon interaction. Such sensitivity will probe new sectors predicted by Supersymmetry with a high discovery potential. The design of XENON1T and R&D projects such as the XENON1T Demonstrator, as well as the future prospect of the field will be discussed in detail.

We will see how a result in von Neumann algebras (a theory developed by von Neumann to give the mathematical framework for quantum physics) gave rise, rather serendipitously, to an elementary but very useful invariant in the theory of ordinary knots in three dimensional space. Then we'll look at some subsequent developments of the theory, and talk about a thorny problem which remains open.